What It Is • Maybe it’s the butter with its rich taste and ability to create tenderness. Or maybe it’s the sugar’s sweetness and caramelized flavor. Or the tenderness of the flour. Or the rich taste created by the eggs. Whatever it is, cake is a treat. Cakes may be light and airy or heavy and dense. But most of all, when compared with other baked goods, cakes are sweet.

Sweetness wasn’t always the defining characteristic of cakes. The first cakes, such as oatcakes, evolved from unleavened breads and crackers. Later cakes, such as panettone, stollen, and fruitcake, evolved from yeast-raised breads. In the 18th century, yeast-raised cakes eventually gave way to sweeter cakes, such as plum cake, pound cake, and sponge cake, raised not by yeast but instead by aerating the batter through prolonged beating of sugar and fat or using an egg white foam to incorporate air bubbles. In the mid-1800s, baking soda and other chemical leaveners lightened the load of strenuous beating and improved the ability of cake batter to rise.

What It Does • In addition to the usual ingredients of eggs, sugar, flour, and fat, a cake is defined by its leavening, which is the method used to create bubbles in the batter. Some cakes use yeast to generate carbon dioxide bubbles. With most cakes, sugar and fat and/or eggs are beaten together to incorporate air into the batter. And some use chemical leaveners to produce carbon dioxide bubbles. Either way, when heated, those bubbles are what makes the cake batter rise.

The exact ingredients, their proportions, and the aeration methods used result in several different styles of cake. In North America, these styles generally fall into two main categories, foam cakes and shortened cakes.

Foam Cakes
For these light and simple cakes, you beat whole eggs and/or egg whites and sugar at length to incorporate air bubbles in the batter, known as a foam. If using only egg whites, the foam should be made in a grease-free glass, stainless steel, or, preferably, copper bowl to ensure maximum aeration. Then you fold in flour gently to avoid deflating the foam and to prevent the formation of gluten in the flour, which would make the cake dense and tough instead of light and tender. You can also incorporate a variety of flavorings, from butter and milk to cocoa powder to flavoring extracts. Foam cakes are baked immediately to capture the maximum leavening effect of the air bubbles in the foam. Foam cakes do not use chemical leaveners. This method produces light, airy cakes such as:

Meringue: Fat-free, this cake is leavened only with aerated egg whites. Dacquoise is a type of meringue cake made with ground nuts and little or no flour and then layered with whipped cream or buttercream.

Angel food: Another fat-free cake leavened only with egg whites. It is essentially a meringue with flour and sugar added.

Sponge: These popular foam cakes are leavened with beaten eggs. Typically, the eggs are separated, the whites are beaten with sugar, the yolks are beaten with sugar and flavorings, then the two foams are gently combined and folded with flour.

French biscuit cake: These cakes are essentially sponge cakes with additional egg yolks. Biscuit cake is the classic cake used for roulades and cake rolls such as bûche de Noël.

Génoise: This French sponge cake is leavened by beating warm whole eggs and sugar until the eggs take on so much air that they resemble whipped cream. Génoise makes a great layering cake, as seen in classic petits fours.

Chiffon: These cakes are remarkable because they combine lightness and richness from a high proportion of whipped egg whites and a fair amount of vegetable oil. The oil makes the cake taste moist and more tender than, say, a biscuit cake. These hybrid cakes also use chemical leaveners for aeration.

Shortened Cakes
Shortened cakes are made by beating sugar and fat together until the fat is filled with air bubbles, a process known as creaming. Butter aerates best at 67°F (19°C); shortening roughly 77°F (25°C). When you cream the sugar and fat, the sugar’s sharp crystalline structure slashes deep pockets in the fat, and those pockets take on air. Then you beat in eggs, one by one, which help to hold even more air. Finally, you fold in flour and usually a chemical leavener such as baking powder or baking soda.

Traditionally the dry ingredients are added with alternate additions of milk, cream, or another liquid so that the flour first gets coated with the beaten fat. This fat coating protects proteins in the flour from being turned into gluten when you stir in the liquid, creating a lower-gluten, more tender cake. An alternative method for making tender shortened cakes, known as the two-stage method, is to combine all of the dry ingredients (flour, baking powder, salt) in one bowl and all of the wet ingredients (eggs, vanilla, milk) in another. You beat the butter and half of the wet ingredients into the dry ingredients to aerate the batter, then beat in the remaining wet ingredients. This method also improves tenderness for the same reason the creaming method does. However, this method makes the cake more likely to toughen from overmixing. Either way, both methods produce several types of rich, moist cake:

Pound cake: Originally calling for a pound each of butter, sugar, flour, and eggs, this cake has evolved to include sour cream, additional egg yolks, and other flavored liquids.

Butter cakes: Rich and moist like pound cake, butter cakes are lighter and more finely textured because of a lower proportion of eggs and fat and a higher proportion of sugar and liquid.

The basic ingredients play key roles in cake making. For instance, cake flour is finely milled, producing a finer crumb in cake. It’s also low in protein, which means it contains less gluten proteins. But some cakes also incorporate almond flour, chestnut flour, other nut flours, or cocoa powder. Cake flour is usually bleached with chlorine, which lowers its pH (makes it more acidic), and causes egg proteins in the batter to coagulate at a lower temperature. It also allows starch in the flour to absorb more moisture, and both of these changes produce a delicate, fine-textured crumb in a very stable structure.

As for the fat, both butter and shortening aerate and tenderize a cake. Fine-textured cakes are created by lots of small gas bubbles. Coarse-textured cakes have fewer, larger gas bubbles. Which type of fat is best? Vegetable shortenings have lots of small fat crystals that can entrap lots of small air bubbles. Butter and lard, on the other hand, have fewer but larger fat crystals that entrap fewer but larger air bubbles. This means that shortenings make lighter, more fine-textured cakes. But butter tastes better. Some bakers use a combination.

Sugars help sweeten cake batter and help it retain moisture. Sugars also tenderize the cake by competing for water and preventing the formation of gluten from the flour. Superfine sugar dissolves more quickly and does a better job of creaming the fat in pound cakes and butter cakes, because it has more fine, sharp edges that pierce more holes in the fat, for a finer texture in the finished cake.

How It Works • Baking transforms batter to cake. The heat of the oven triggers many of the chemical processes that create a cake’s defining textures and flavors. Each of the key ingredients — fat, sugar, flour, eggs, and chemical leaveners — is affected.

Yeast-raised cakes and those using baking powder or other chemical leaveners produce carbon dioxide that migrates to the air bubbles incorporated into the batter. When heated during creaming, the gases expand and make the cake rise. Even cakes with no chemical leaveners, such as angel food cake, have enough air bubbles from the egg white foam to expand in the oven’s heat and raise the cake. Water in the batter also changes to steam and expands, contributing to the rise.

In the oven, gas bubbles expand and mature. By this point in the baking, the cake’s structure should be set and when cooled creates a solid foam. If the oven is set too low and the batter heats too slowly, the gas bubbles overexpand before the cake sets, creating a large-holed, coarse-grained texture in the finished cake.

Keep in mind that altitude and atmospheric pressure also affect the baking, particularly the expanding gas bubbles. As altitude increases, there is increasingly less atmospheric pressure, which allows the leavening gases to expand more rapidly, stretching and weakening the structure of the cake, which can result in a coarse texture or cause the cake to fall. Cakes baked at high altitudes (above 3,000 feet/914 m) use lower oven temperatures and less leavening agent.

The cake batter sets, in part, because eggs and flour contain protein that coagulates, or firms up, when heated (at about 180°F/82°C). The liquid in the batter, such as milk, cream, water, and even eggs (which are about 74% water), also hydrates the starch in the flour when it is heated. As the starch granules absorb moisture and swell, they form a paste, which then stiffens or sets. This process is known as gelatinization and is followed by gelation (forming of a gel) upon cooling.

The fat (shortening, oil, or butter) in the batter tenderizes the cake. When heated, the fat melts, releases the air it once held, and slides into the coagulated and stiffened structure of the cake, tenderizing and moistening it. Shortening contains emulsifiers that do a better job than butter of dispersing fat throughout the batter. Regardless of whether you use butter, shortening, or oil, more fat in a cake weighs it down and makes it heavier. Call to mind the dense texture of fat-rich pound cake. Less fat, on the other hand, allows the gas bubbles to expand more in the oven, creating the more open, airy texture of angel food and sponge cakes.

Sugar delivers the characteristic sweetness of cakes but also tenderizes them by competing for available water that’s also necessary for gluten formation and starch gelatinization. Sugars and proteins combine in the Maillard reactions, browning the cake’s surface and developing hundreds of new flavor compounds that we recognize as delicious.

The heat level is important, too. Most cakes are baked at a moderate 350°F (180°C). If the oven is too low, the fat melts so quickly that it releases its leavening gases before the other elements in the batter set, preventing the cake from rising. If the heat is too high, the crust forms before the center is set, causing a soggy center with gases that continue to expand late in the baking process, which can crack the crust. Keep an oven thermometer in your oven for accurate temperature measurements.

Now that we’ve discussed ingredients, mixing, and baking, the cake is ready to eat, right? Well, cooling and storing also affect the finished product. Cakes need to cool to allow the flour’s gelatinized starch to gel and firm up the cake. If removed too soon, the cake may stick to the pan. If left in the pan too long, the cake will steam so much that it becomes soggy. Shortened cakes should be cooled in the pan on a wire rack for five to 10 minutes to allow cool air to circulate beneath the pan bottom and speed cooling. Then remove the cake from the pan and let it cool completely on a wire rack to allow excess steam to escape into the air. Angel food, chiffon, and sponge cakes should be cooled completely upside down in the tube pan to avoid crushing their delicate foam.

Cakes keep well at room temperature for a few days because of their fat and their sugar, which retain moisture. Refrigerating cakes tends to dry them out, but they freeze well, especially if they are high in fat. Wrap completely cooled cakes tightly in plastic wrap to prevent air from reaching the cake and speeding spoilage.

Fast fact
• In 1927, Harry Baker, an insurance salesman and part-time Hollywood caterer, invented the chiffon cake, a type of sponge cake made with oil instead of butter. He sold the formula to General Mills in the 1940s.

Science wise
"Red Chocolate"
Devil’s food cake (and, to some extent, red velvet cake) gets its ruddy color from the addition of baking soda, which increases the alkalinity of cocoa to pH 7.5 and turns the cocoa pigments dark red. Too much baking soda can cause a bitter or soapy aftertaste.

Kitchen wisdom
Three Tips for Better Cakes

• To brighten a cake’s flavor, include at least 1⁄2 teaspoon (2 mL) salt in a typical 10-serving cake.

• To make fine-textured angel food cake, add cream of tartar to the egg whites, which lowers the pH, stabilizing the egg-white foam and whitening the flour pigments.

• To quickly grease cake pans, use nonstick baking spray, a mixture of fat and flour. Or make your own baker’s grease by stirring together 1 cup (250 mL) plain vegetable shortening and 1⁄2 cup (125 mL) flour. Refrigerate the mixture indefinitely and use in place of butter and flour for greasing pans.

Reprinted with permission from THE SCIENCE OF GOOD FOOD (click link to purchase)
Text copyright 2008: David Joachim and Andrew Schloss
Published by Robert Rose Inc. 2008

Dr. Phil Handel is the Program Director for Drexel's Hospitality Management, Culinary Arts, and Food Science program.

"Science of Good Food" photograph by Horia Varlan via Flickr (Creative Commons); "Plate" photograph from FoodCollection/Getty Images.